The invention concerns a process for the production of carbon black in a flow reactor by spraying a hydrocarbon containing liquid feedstock by means of a propellant gas into a stream of hot reaction gases produced by burning a fuel as well as an apparatus for carrying out the process.
For the production of finely divided carbon blacks which are versatilely used as reinforcing fillers and black pigments the furnace black process is of even greater significance because of its industrial efficiency and versatility.
In the furnace black or oven black process a mostly gaseous fuel is burned with an oxygen containing gas (air) in a closed, fire resistant lined reactor in order to produce the temperatures necessary for the formation of carbon black. The feedstock, generally an aromatic oil, is nozzled in the hot flue gases formed thereby. The feedstock vaporizes and is changed by cracking and partial combustion into carbon black and flue gases which themselves still contain burnable components. After the completion of the carbon black forming reaction the carbon black-flue gas mixture is quenched by spraying in water. The furnace black process, since it is carried out in closed apparatus, is environmentally desirable and permits the production of carbon blacks of different particle sizes and structure with high capacity. Because of the advantages which are exhibited compared to other processes of producing carbon black there has been constant work to shape the process still more flexibly in order to make it possible to produce carbon blacks for all fields of use exclusively by the carbon black process.
It is known that to produce both high quality furnace blacks and also high abrasion resistance rubber blacks a very rapid vaporization and mixing in of the liquid carbon black feedstock into the reaction gases is necessary.
In order to make possible a quick vaporization of the carbon black feedstock it is finely divided with the help of atomizing nozzles. Both binary and unary nozzles are used.
A typical form of an injector for liquid carbon black feedstock with a binary nozzle is described in German AS No. 1,625,206 (or related Kuhner U.S. Pat. No. 3,701,480). In that patent the carbon black feedstock is brought in in a state of acceleration caused by a propellant gas (atomizing gas) and leaves an aerosol from a cylindrical or Laval shaped nozzle. Carbon black feedstock and propellant gas thereby are under increased pressure. With such or similar arrangements there is indeed obtained a very fine distribution of the carbon black feedstock and therewith a high vaporization velocity. However, it is disadvantageous that the carbon black feedstock-propellant-mixture thereby leaves in a restricted manner in a strongly concentrated free jet (opening angle about 15.degree.). As a result the mixing in of the reaction gases produced by burning the fuel is limited in a relatively slow and non-uniform manner.
While the carbon black formation already has begun in the peripheral zones of the free jet encased by the reaction gases, in the nucleus of the jet a thorough mixing with the reaction gases has not yet occurred.
Other process variants use for atomization of the carbon black feedstock unary nozzles in which the carbon black feedstock is atomized without the help of a propellant, in most cases in the form of a hollow cone. These atomizing nozzles offer the advantage that the feedstock can leave with large spraying angles and be distributed over a large surface area so that it makes it easier to have a thorough mixing with the reaction gases. On the other hand, the disadvantages are that a unary atomization leads to substantially larger liquid drops than the binary atomization so that the vaporization speed of the liquid carbon black feedstock is reduced. A more serious disadvantage to lower vaporization speed is the formation of coke which both can occur in the free reaction space of the furnace and lead to small coke particles (grit) in the carbon black and also can lead to greater coke deposits on the walls of the reactor. The problem of the coke deposits on the reactor walls occurs especially strongly with relatively narrow and highly loaded furnaces.